The present invention relates to an electronic throttle valve control apparatus suitable for use in a car engine and more particularly to a car throttle valve control apparatus suitable for controlling a throttle valve by using a motor.
As a conventional car throttle valve control apparatus, an electronic throttle valve control apparatus has been known in which for adjustment of intake air flow sucked into an engine, a throttle valve attached to an intake manifold is controlled by a motor.
Generally, as described in, for example, JP-A-8-303285, for control of the opening of the throttle valve, the opening of the throttle valve is detected by means of, for example, a potentiometer connected directly to a rotary shaft of the throttle valve under the control of a microcomputer and the detected opening is inputted to the microcomputer through an A/D converter to perform operational control which makes the detected opening coincident with a target opening.
A technique as described in, for example, JP-A-6-54591 has also been known, according to which current flowing through a motor for rotating a throttle valve is chopper-controlled by means of, for example, an H-bridge chopper circuit comprised of power MOS FET""s, the current flowing through the motor is detected and fed back to a microcomputer and a result of the feedback control operation is delivered out of the microcomputer in the form of a PWM signal to control the opening of the throttle valve.
Conventionally, for control of the throttle valve, both the opening control (position control) and the current control are effected using the microcomputer. For the purpose of improving the performance of the electronic throttle valve, the response speed of the opening control is required to be increased and to this end, a high-speed microcomputer capable of processing operations in high speed is needed. Especially, when the current control involved in a minor loop of the opening control is desired to be carried out with a microcomputer, it is inevitable that the microcomputer will be a high-speed one.
But the high-speed and high performance microcomputer is expensive, and when it is used for the electronic throttle valve, the control apparatus becomes costly as a whole and a cheap control apparatus cannot be provided.
An object of the present invention is to provide an inexpensive electronic throttle valve control apparatus in which an electronic throttle valve apparatus does not require an expensive microcomputer but uses an inexpensive microcomputer.
Another object of the present invention is to provide a throttle valve control apparatus for a car in which the accuracy of control can be improved by increasing the response speed in motor current control.
Still another object of the present invention is to provide a throttle valve control apparatus in which even when power elements of low switching speed are used in an H-bridge chopper adapted to control a motor, a response delay in switching can be compensated for.
A car electronic throttle valve control apparatus according to the present invention comprises a throttle valve, a motor for driving the throttle valve, an H-bridge chopper for chopper-controlling current flowing through the motor to control rotation of the motor, an analog current control unit for supplying a pulse-width modulation (PWM) control signal to the H-bridge chopper, a current detection unit for detecting the motor current and feed-backing it to the analog current control unit, a control unit for controlling the opening of the throttle valve by supplying a current command signal and a forward or backward rotation signal for the motor to the analog current control unit through a filter, a unit for detecting an opening of the throttle valve and feed-backing it to the opening control unit, and a unit for supplying an opening command for the throttle valve. The opening control unit responds to the opening command and the opening feedback signal to generate the current command supplied to the analog current control unit. The analog current control unit responds to the current command and the motor current feedback signal to change the PWM control signal supplied to the H-bridge chopper, so that the motor is rotated while the motor current being controlled by means of the H-bridge chopper so as to control the opening of the throttle valve.
In the car engine throttle valve control apparatus, the current control unit is an analog unit comprised of operational amplifiers and including a PWM generator circuit, a current detection circuit and a current difference operation circuit.
The PWM generator circuit may be a variable frequency type PWM circuit comprised of an integrator and a comparator.
The current detection circuit is connected to a battery current detecting resistor connected in series with the H-bridge chopper and includes an amplifier for amplifying a voltage developing across the current detection resistor and an A/D converter for converting the voltage signal into a digital signal.
The current detection circuit further includes a sample-hold circuit for sample-holding the amplified signal in synchronism with the fall of the analog PWM signal.
The throttle valve opening control unit includes a circuit which receives, under the control of a microcomputer, an opening command from a master engine control unit through a communication circuit and a feedback signal indicative of a throttle valve opening to perform a control operation and delivers a current command in the form of an analog signal through a D/A converter, or a circuit for generating a current command in the form of a duty ratio signal in the PWM mode to have control of only an opening control operation.
The throttle valve opening control unit uses an inexpensive low-speed microcomputer of slow operation processing to generate a command value of motor current and a forward or backward rotation signal for the motor, which are necessary for controlling the opening, so as to control only the throttle valve opening.